One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disk drive. The most basic parts of a disk drive are a disk that is rotated, an actuator that moves a transducer to various locations over the disk, and electrical circuitry that is used to write and read data to and from the disk. The disk drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disk surface. A microprocessor controls most of the operations of the disk drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disk.
The transducer is typically housed within a small ceramic block. The small ceramic block is passed over the disk in a transducing relationship with the disk. The transducer can be used to read information representing data from the disk or write information representing data to the disk. When the disk is operating, the disk is usually spinning at relatively high RPM. These days common rotational speeds are 7200 RPM. Some rotational speeds are as high as 10,000 RPM. Higher rotational speeds are contemplated for the future. These high rotational speeds place the small ceramic block in high air speeds. The small ceramic block, also referred to as a slider, is usually aerodynamically designed so that it flies over the disk. The best performance of the disk drive results when the ceramic block is flown as closely to the surface of the disk as possible. Today's small ceramic block or slider is designed to fly on a very thin layer of gas or air. In operation, the distance between the small ceramic block and the disk is very small. Currently "fly" heights are about 12 micro inches. In some disk drives, the ceramic block does not fly on a cushion of air but rather passes through a layer of lubricant on the disk.
Information representative of data is stored on the surface of the memory disk. Disk drive systems read and write information stored on tracks on memory disks. Transducers, in the form of read/write heads, located on both sides of the memory disk, read and write information on the memory disks when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disk. The transducer is also said to be moved to a target track. As the memory disk spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the memory disk. Similarly, reading data on a memory disk is accomplished by positioning the read/write head above a target track and reading the stored material on the memory disk. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disk drives, the tracks are a multiplicity of concentric circular tracks. In other disk drives, a continuous spiral is one track on one side of a disk drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
One of the most critical times during the operation of a disk drive is just before the disk drive shuts down. The small ceramic block is typically flying over the disk at a very low height when shutdown occurs. In the past, the small block was moved to a non data area of the disk where it literally landed and skidded to a stop. Problems arise in such a system. When disks were formed with a smooth surface, stiction results between the small ceramic block and the disk surface. In some instances, the force due to stiction are large enough that the head would be virtually ripped away from the suspension. Amongst the other problems was the limited life of the disk drive. Each time the drive was turned off another start stop contact cycle would result. After many start stop contacts, the small ceramic block may chip or produce particles. The particles could eventually cause the disk drive to fail. When shutting down a disk drive, several steps are taken to help insure that the data on the disk is preserved. In general, the actuator assembly is moved so that the transducers do not land on the portion of the disk that contains data. There are many ways to accomplish this. A ramp on the edge of the disk is one design method that has gained industry favor more recently. Disk drives with ramps are well known in the art. U.S. Pat. No. 4,933,785 issued to Morehouse et al. is one such design. Other disk drive designs having ramps therein are shown in U.S. Pat. Nos. 5,455,723, 5,235,482 and 5,034,837.
Typically, the ramp is positioned to the side of the disk. A portion of the ramp is positioned over the disk itself. In operation, before power is actually shut off, the actuator assembly swings the suspension, slider and transducer to a park position on the ramp. When the actuator assembly is moved to a position where parts of the suspension are positioned on the top of the ramp, the sliders or ceramic blocks do not contact the disk. Commonly, this procedure is referred to as unloading the heads. Unloading the heads helps to insure that data on the disk is preserved since, at times, unwanted contact between the slider and the disk results in data loss on the disk. The actuator assembly may be provided with a separate tang associated with each head suspension. The tang may ride up and down the ramp surface. In other drives, the ramp may be positioned such that the suspension rides up and down the ramp to unload and load the disk or disks of the disk drive.
Many of the disk drives that feature ramps have one or two disks. Tolerances were not a major problem in such designs since there was not much variation in the tolerances associated with the various components, namely the disk stack, the disks, the ramp or the suspension. In other words, in the one and two disk stack disk drive designs, the tolerances could be controlled so that the various components fit together without problems.
There is a constant trend in the disk drive industry toward higher capacity magnetic disk memory. To attain higher capacity, drives are now being populated with multiple stacked disks. Track densities and total data capacity can be increased using highly polished, smooth disks. The higher number of disks generally have to be placed within the same dimension as a lower number of disks. Thus, interdisk spacing gets smaller and smaller. Furthermore, more disks means more parts and therefore the tolerances associated with each of the separate parts can add up to provide for wide variance for the various dimensions of the disk stack.
To use the smooth disks in a multidisk stack, there is a need for a ramp structure that can be used to load transducers to the disk and unload transducers from the disk. Each disk surface requires a ramp. A load/unload structure must therefore be formed having multiple ramps which are registered to the disk surfaces of each disk in the disk stack. Many of the components of the drive are made from separate parts. As mentioned previously, the disk stack is formed from many parts which each have a separate tolerance. Individual disks are stacked on a hub. Spacers are used between the disks. The hub, disk spacers and disks each are formed within a specified tolerance. These tolerances can stack up differently for each disk stack assembly. Other components made from separate parts, can also have stack up tolerances. These other components may include the load/unload mechanism, and the E-block of the actuator which holds all the separate head gimbal assemblies.
Overcoming tolerance problems is a constant problem faced in designing and assembling disk drives. The placement of ramps near the disks is one area of the drive where potential tolerance mismatches due to tolerance stack up from several components within the disk drive may cause problems. When the actuator moves E-block to unload the sliders from the disks or to load the sliders onto the disks in the drive, three components must meet. Namely the actuator E-block, the load and unload structure (typically a ramp assembly), and the disk stack. Each of the three may have a potential stack up tolerance which could result in a mismatch with respect to the other components.
A tolerance mismatch between the any of the three separate components with separate stack up tolerances would result in the components not fitting with one another or an interference between components. For example, a suspension attached to an arm of the actuator may strike the end of a ramp rather than ride up the ramp surface. In this case, all the sliders and the transducers held by the sliders would not be able to be parked off the surface of the disk. Another example would be to allow the actuator E-block and the sliders and transducers attached to the E-block to move with respect to the disks and the ramps, but to do so with excessive interference. In other words, the actuator could move the E-block as intended but with less than optimal efficiency.
In order to insure that the actuator can move the E-block with respect to the disk and the ramp as intended, it appears that there is a need for a system which has some adjustability in one or more of the parts. This is further necessary in light of the fact that as interdisk spacing gets smaller, the tolerances associated with the disk stack are becoming tighter. In addition, the components are becoming much more sensitive to slight shock loading or to thermal effects. The small ceramic blocks which contain a transducer are now smaller than ever before. Gimbal springs must allow for gimballing of the small ceramic blocks and are therefore much more sensitive to slight shock loading. A slight shock load can effect a suspension so that the z-height may be off slightly. Similarly, small tilt angles can result in the arms of the actuator. Since the components are more sensitive to such changes, it is necessary to also allow for some adjustability in one or more components of the actuator.